1. Field of the Invention
The invention relates to a filter arrangement for a tank ventilation system of a fuel tank. The filter arrangement has a housing with a tank-side fuel vapor inlet opening, an engine-side fuel vapor outlet opening, an atmosphere opening and has at least one first adsorption region.
2. Description of the Related Art
Filter arrangements for a tank ventilation system are well known in the motor vehicle industry and are used to reduce evaporative emissions. Emissions of this type can arise, for example, by fuel vapor being produced by high temperature changes over the course of a day. It is also possible that, after a journey at high speed, the heat of the engine is conducted to the fuel tank and produces the fuel vapor. Of course, fuel vapor also arises during refueling. To prevent the fuel vapor from being output to the atmosphere, the fuel vapor is fed via a tank-side fuel vapor inlet opening to the filter arrangement and, on the way to the atmosphere opening, flows through a housing that is filled with adsorbents that adsorb the hydrocarbon molecules in the fuel vapor. Accordingly, cleaned air can leave the filter arrangement via the atmosphere opening.
The filter arrangement is cleaned and/or emptied by opening an engine-side fuel vapor outlet opening via a valve arrangement in the fuel-operated driving mode. A negative pressure prevails at the opening and ensures that ambient air is fed via the atmosphere opening to the filter arrangement and, during the passage through the adsorption region, detaches the accumulated hydrocarbon molecules again and feeds the molecules to the combustion air for subsequent combustion.
A multiplicity of documents are concerned with optimizing the adsorption of fuel vapor, and an excessive pressure differential from the fuel vapor inlet opening to the atmosphere opening has been perceived to be the main problem. To improve the adsorption operation, it is known, for example, from U.S. Pat. No. 6,540,815 B1, to provide various adsorption regions in the housing of a filter arrangement. The adsorption capacity decreases ever further, as seen in the direction of flow, from the fuel vapor inlet opening toward the atmosphere opening. More particularly, at the fuel vapor inlet opening or fuel vapor outlet opening there is an adsorption region that has a very high absorption capacity and, at the atmosphere opening, there is an absorption region having a very small absorption capacity.
A filter arrangement designed in such a manner delivers good results for the absorption of gaseous hydrocarbon molecules. However, such a filter arrangement has become problematic against the background of developing highly modern combustions engines or hybrid engines, optimally to control the purging operation of the filter arrangement. For example, in the case of hybrid engines, the operating times for a purging operation are extremely limited because of the switching off of the internal combustion engine. Furthermore, all types of engines are activated evermore precisely in respect of the fuel/air mixture, which results in a large outlay in terms of control technology for the purging operation to avoid too lean or too rich a fuel mixture.
It is therefore the object of the invention to provide a filter arrangement that assists and ensures the regulation of the internal combustion engine during the purging operation of the filter arrangement in a simple and cost-effective manner.